Meanwhile SP21 has been delivered which contains support for oauth:https://experienceleague.adobe.com/en/docs/experience-manager-65/content/release-notes/release-notes#foundation-integrations-6521 A hotfix for lower versions is available for download via the Software Distribution page.

We are having the same issue after migrating from JWT to OAuth. I'm unable to find any documentation on how to migrate our on-prem AEM to this new authentication. Adobe-Target-IMS-IO: failed to get access token from authorization server status: 400 response: {"error_description":"The client must hav...